Experimental investigation of wood chip gasification using downdraft fixed bed gasifier

Abstract: Gasification is a thermo-chemical process to convert carbonaceous materials into gaseous products which could be used as a fuel in engines for power generation or in boiler for heat supply. This paper investigated the effect of equivalence ratio (ER) on the gasification performance in terms of the temperature in the gasifier, the composition distribution of the producer gas, and the tar content in the producer gas using a lab-scale downdraft fixed bed gasifier fed by Pinus sylvestris wood chips. In addition, the characteristics of gasification byproducts, namely bio-char and bio-tar, were analyzed. The proximate and ultimate analysis, the surface morphology, the surface area, and the pore size distribution of wood charcoal were obtained by the scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method. The components of light tar and heavy tar were obtained by the gas chromatography-mass spectrometry (GC-MS). The results showed that the optimal ER was 0.251 with the maximum LHV of producer gas (4.55 MJ/Nm3 along with CO of 17.47%, H2 of 14.67%, CO2 of 12.43%, and CH4 of 2.12%), a minimum tar content of 350 mg/Nm3, and a maximum cold gas efficiency of 65.46%. The charcoal was a porous material with a high heating value of 28.17 MJ/kg and a high BET surface area 342 m2/g which could potentially be feedstock for the production of briquettes fuel and activated carbon. The light tar was mainly composed of phenols (36.75%), acetic acid (22.14%) and ketones (13.73%). After refining and dilution, the light tar could be a potential substance to produce plant growth regulator. The heavy tar was mainly composed of heterocyclic aromatics (59.98%), light aromatics (1 ring) (4.71%) and light polycyclic aromatic hydrocarbons (2-3 ring) (16.48%). The heavy tar could be a potential feedstock for aromatic chemicals production.